A reaction in a calorimeter containing 80.0 g of water at 20 degrees Celsius causes the temperature to fall by 1.5 degrees. what is the thermal energy of the water? I got 6.2 J or 6192.32 kJ but they say 5.02 x 10^4 kJ idk what I am doing wrong
q=mc(delta-T) = 80g(4.184j/g-C)(1.5 C)= 502 joules x (1 Kj/1000 joules) = 0.00502 Kj = 5.02E-4Kj
To calculate the thermal energy of the water, you need to use the heat capacity equation:
Q = mcΔT
where:
Q = thermal energy (in joules)
m = mass of water (in grams)
c = specific heat capacity of water (in J/g°C)
ΔT = change in temperature (in °C)
Given:
m = 80.0 g
ΔT = -1.5 °C (negative because the temperature fell)
The specific heat capacity of water is approximately 4.18 J/g°C, so we substitute the values into the equation:
Q = (80.0 g)(4.18 J/g°C)(-1.5 °C)
Q = -498.6 J
The negative sign indicates that the water lost thermal energy. However, since the question asks for the thermal energy without specifying the sign, we consider the absolute value:
|Q| = 498.6 J
Thus, the thermal energy of the water is approximately 498.6 J, not 6.2 J or 6192.32 kJ. The given answer of 5.02 x 10^4 kJ appears to be incorrect.
To calculate the thermal energy of the water, we need to use the formula:
q = m * c * ΔT
Where:
q is the thermal energy (in joules)
m is the mass of the water (in grams)
c is the specific heat capacity of water (4.18 J/g°C)
ΔT is the change in temperature (in °C)
In this case, the mass of the water (m) is given as 80.0 g and the change in temperature (ΔT) is given as -1.5 °C (negative because the temperature falls).
Let's substitute these values into the formula:
q = 80.0 g * 4.18 J/g°C * -1.5 °C
q = -501.6 J
Now, it seems you calculated the thermal energy as positive, which is why you obtained 6.2 J (positive). However, since the temperature is falling, the thermal energy should be negative. Therefore, -501.6 J is the correct answer in joules.
Now, to convert joules to kilojoules, divide the answer by 1000:
-501.6 J / 1000 = -0.5016 kJ
The correct answer for the thermal energy of the water is approximately -0.5016 kJ. However, keep in mind that the negative sign indicates a decrease in thermal energy due to the decrease in temperature.